Cool water residual in the pipe needs to drain out before user gets shower, especially in winter. User can then get shower with warm water. Traditional technology to drain cool water out is by manual control, that is to say, the user needs to switch the valve to warm water to wait the cool water draining out, in some area, this process may need a few minutes; this method also needs the user using his hand to touch and test the water temperature and waits, otherwise he might get chilly; he needs to spend time on waiting, if he doesn't wait beside, hot water might be wasted. A switch valve with cool water draining function is disclosed in Chinese patent database with application number 20151135958.8, the switch valve is disposed with a cool water draining passage, cool water residual in the outlet waterway can drain out by the cool water draining passage by controlling the outlet waterway to connect to the cool water draining passage; when water flows out of the outlet waterway normally, the cool water draining passage is closed. To achieve above mentioned effect, a check valve and a reset spring are disposed to open and close the connection of the outlet waterway and the cool water draining passage. firstly, as the check valve is normal-close, the check valve is open by a certain suction force, the suction force needs to overcome the elastic force of the spring and the friction force of the check valve and the Y-ring; secondly, the direction of the suction force by Venturi effect is parallel to the moving direction of the check valve when draining cool water, but the section area is small, the action area of the suction force to the check valve is small, the downward force acted on the check valve is also small, if the force is smaller than a certain value, the check valve can not be open, cool water can not drain out of the showerhead waterway; thirdly, to increase the suction force, the proportion of the section area of the cool water draining passage and the mutation chamber is increased; to reduce the product size, it needs to reduce the section area of the cool water draining passage, resulting in low flowing area of the cool water draining mode and low flow volume and thus lengthened cool water draining time; Fourthly, as the friction force of the Y-rings and the side wall of the check valve are large, although there is restoring force of the spring, the check valve is difficult to reset; as the check valve can not perfectly reset, when the showerhead works, water will flow to the handheld showerhead through the air suction hole, resulting leakage of the handheld showerhead. In addition, when the handheld showerhead works, if the handheld showerhead has small volume outlet or water stop function, the pressure in the cool water draining passage would increase, water flowing through the handheld showerhead would flow to the showerhead from the air suction hole, resulting in leakage of showerhead. This kind structure is not reliable.